The studies presented in this application are based on previous observations that 1) the post-ischemic infusion of adenine nucleotides-MgCl2 will effectively accelerate the recovery of inulin clearance, 2) during recovery from acute renal injury, superficial single nephron function returns to normal values while whole kidney function remains reduced and 3) this pattern of recovery can be enhanced by treatment with ATP-MgCl2. The objectives of the proposed studies are 1) to define the mechanisms of recovery of single nephroin function of glomerular filtration dynamics following an ischemic renal insult, 2) to determine the reason for the discrepancy in the rate of recovery of single nephron and whold kidney function and 3) to investigate th physiologic mechanisms through which ATP-MgCl2 has a salutory effect on process of recovery from an ischemic renal insult. Using micropuncture and morphologic techniques, four aspects of the recovery process will be studied. To evaluate the role of altered tubular permeability, back-leak of microinjected inulin and horseradish peroxidase will be studied. Proximal tubular hydrostatic pressure will be determined using a servonulling device to asses the presence of intratubular obstruction. The heterogeneity of recovery of nephron function will be evaluated by the intravenous infusion of horseradish peroxidase and sampling of both superficial and deep nephrons for morphologic study. The possibility of preferential reperfusion of outer cortical nephrons will be defined by comparing renal plasma flow in superficial nephrons, determined by micropuncture techniques, to whole kidney plasma flow. Each of these aspects of the recovery process will be studies with and without enhancement by ATP-MgCl2. Because the infusion of adenine nucleotides-MgCl2 has been effective when given after the acute insult, studies designed to define the physiologic mechanisms through which these agents have been effective offer the opportunity to study renal responses which may have potential applicability in the design of therapeutic programs or the development of improved methods for organ preservation.